aisi section d3.2.1

huangyhg

aisi section d3.2.1
is anyone familiar with section d3.2.1 of the 1996 aisi cold formed design manual and its applicability to a through fastened roof?  
the load pl that is calculated in this section is not very clearly defined. is this the load that must be resisted by each purlin brace only along the roof slope, or does the load become additive (cumulative) along the slope of the roof. also, with regards to the w used in the calculation, i am assuming that this is the load supported by all purlins in the roof and not a single purlin line. is this accurate?
any light you can shed on this section is appreciated.
thanks,
js.
does anyone have any input on this?
thanks,
js.
i agree it is not clear.  this is my take on it for the brief time i've looked at this section.  i'm not saying i'm 100% sure but this is what i've come up with.
the weight w is the total weight supported by all the purlins for that particular slope.  since the pl equation takes into account the number of purlins being supported (np) and the weight w is the total weight being supported by all the purlins, i would say pl is not cumulative.   
a diagram in the code here would go a long way to help understand this.